PHOTOSYNTHESIS Sun Hwa Dong

Photosynthesis Produces organic substances Uses light Energy, Simple inorganic substances Light Energy to Chemical Energy

Absorption of Light Sunlight = White light, but made up of wavelengths like red, green, blue Pigments absorb lights Red, Blue > Green Green light cannot be reflected

Absorption of Energy Some used to produce ATP. Some split water molecules – Photolysis of Water This forms Oxygen and Hydrogen.

CO ₂ is absorbed to make organic substances. Carbon in a gas to carbon in solid compounds – Carbon Fixation This involves use of Hydrogen from photolysis and Energy from ATP.

Measuring Rates of Photosynthesis Production of O ₂ : Aquatic plants release bubbles of O ₂ Uptake of CO ₂ :If CO ₂ is absorbed from water, the pH of water rises Increases in biomass : the rate of increase in biomass means more photosynthesis.

Effect of Light Intensity

Effect of CO ₂ Concentration Low light intensity - shortage of ATP and hydrogen

Effect of Temperature CO ₂ fixation is catalyzed by enzymes.

Limiting Factors Each factors can limit the rate when below optimal level. Combination of factors – only one factor furthest from its optimum limits When 2 of the factors are equally close to optimum, increasing them rises the rate.

Action and Absorption Spectra Action Spectra: % use of wavelengths of light in photosynthesis Absorption Spectra: % use of the wavelengths of visible light that are absorbed

Photoactivation Chlorophyll & accessory pigments - Photosystem Chlorophyll molecules in photosystem absorb light energy and pass it to 2 special chlorophyll molecules in the reaction centre. Electron within the molecules become excited and photoactivated.

Photophosphorylation Photophosphorylation: the production of ATP, using E from light which is carried out by thylakoids Thylakoids: regular “stack” of membranes that contain Photosystem I & Ⅱ, ATP synthase, a chain of electron carriers

Chemiosmosis 1. Protons pass across membrane and release E which is used by ATP synthase to produce ATP. 2. The coupling of ATP synthesis to electron transport via a concentration gradient of protons → CHEMIOSMOSIS

Chloroplasts structure Chloroplast envelop Thylakoids Small fluid filled spaces inside Thylakoids Mostly have stacks of thylakoids called grana Colorless fluid around Thylakoids = stroma

Bibliography Course Companion p Study Guide p21, p75,p76-81 Pearson: p 74-78, p Pearson Education, Inc., publishing as Benjamin Cummings micro.magnet.fsu.edu/.../chloroplasts.html

Vocabulary Photosynthesis: The process used by plants and other organisms to produce all their own organic substances (food), using only light energy and simple inorganic substances. Photolysis of water: Splitting of water by energy absorbed by chlorophyll. Carbon Fixation: The conversion of carbon in a gas to carbon in solid compounds. Photosystem: protein complexes involved in photosynthesis Photoactivation: The initial stage of photosynthesis in chlorophyll Molecules where the presence of light Energy raises the energy. Chemiosmosis: The coupling of ATP synthesis to electron transport via a concentration gradient of protons Photophosphorylation: the production of ATP, using E from light which is carried out by thylakoids Thylakoids: regular “stack” of membranes with very small fluid-filled spaces inside that contain Photosystem I & Ⅱ, ATP synthase, a chain of electron carriers Grana: stacks of thylakoids Stroma: a colorless fluid around the thylakoids that contains many different enzymes